1. Field of the Invention
The present invention is related to a spectral device and a confocal scanning microscope provided with the spectral device.
2. Description of the Related Art
At present, a microscope provided with a spectral device which acquires wavelength information about light by dispersing and detecting light from a sample has become dominant in the field of a fluorescent microscope. Since the fluorescence detected by a fluorescent observation is very feeble, high detection efficiency is required for the spectral device included in a fluorescent microscope.
In a spectral device, light is generally dispersed by a diffraction grating which is designed so that the diffraction efficiency of primary diffracted light (hereafter referred to as primary diffraction efficiency) may be higher. Recently, a spectral device which realizes high detection efficiency of about 80% has been developed by adopting a diffraction grating having high primary diffraction efficiency.
In addition, from a point of view different from the improvement of a unit performance of a diffraction grating, a technique of realizing a spectral device having high detection efficiency has also been studied. For example, in the Japanese Laid-open Patent Publication No. 2007-286043, a technique of re-using zeroth-order diffracted light generated by a diffraction grating is disclosed. The spectral analysis unit disclosed by the Japanese Laid-open Patent Publication No. 2007-286043 has a configuration of circulating a zeroth-order diffracted luminous flux by leading the zeroth-order diffracted luminous flux generated by a diffraction grating to the diffraction grating with a mirror.
A diffraction grating has the characteristic of changing a peak wavelength to the diffraction efficiency which is depending on the angle of incidence. Therefore, to detect the fluorescence of a requested wavelength depending on the fluorescent substance etc. with high efficiency, it is requested that the spectral device is configured to change an angle of incidence by rotating a diffraction grating.